In conventional petroleum processes, alkylate is typically used to describe a product formed by an alkylation process involving an isoparaffin-containing feed and an olefin-containing feed. Industrially, alkylation reactions often correspond to the reaction of a C2 to C5 olefin, normally 2-butene, with isobutane in the presence of an acidic catalyst to produce a so-called alkylate. This alkylate is a valuable blending component in the manufacture of gasoline due not only to its high octane rating but also to its sensitivity to octane-enhancing additives, especially in light of increasing demand for higher octane and lower Reid Vapor Pressure (RVP) gasoline. Industrial isoparaffin-olefin alkylation processes have historically used hydrofluoric or sulfuric acid catalysts under relatively low temperature conditions. The sulfuric acid alkylation reaction is particularly sensitive to temperature, with low temperatures being favored to minimize the side reaction of olefin polymerization. Acid strength in these liquid acid catalyzed alkylation processes is typically maintained at 88 to 94 weight percent by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature sensitive and the acid is more easily recovered and purified. A general discussion of sulfuric acid alkylation can be found in a series of three articles by L. F. Albright et al., “Alkylation of Isobutane with C4 Olefins”, 27 Ind. Eng. Chem. Res., 381-397, (1988). For a survey of hydrofluoric acid catalyzed alkylation, see 1 Handbook of Petroleum Refining Processes 23-28 (R. A. Meyers, ed., 1986). An overview of the entire technology can be found in “Chemistry, Catalysts and Processes of Isoparaffin-Olefin Alkylation—Actual Situation and Future Trends, Corma et al., Catal. Rev.—Sci. Eng. 35(4), 483-570 (1993).
Both sulfuric acid and hydrofluoric acid alkylation share inherent drawbacks including environmental and safety concerns, acid consumption, and sludge disposal. Research efforts have, therefore, been directed to developing alkylation catalysts which are equally as effective as, or more effective than, sulfuric or hydrofluoric acids but which avoid many of the problems associated with these two acids.
U.S. Pat. No. 3,644,565 discloses alkylation of a paraffin with an olefin in the presence of a catalyst comprising a Group VIII noble metal present on a crystalline aluminosilicate zeolite having pores of substantially uniform diameter from about 4 to 18 angstrom units and a silica to alumina ratio of 2.5 to 10, such as zeolite Y. The catalyst is pretreated with hydrogen to promote selectivity.
U.S. Pat. No. 4,384,161 describes a process of alkylating isoparaffins with olefins to provide alkylate using a large-pore zeolite catalyst capable of absorbing 2,2,4-trimethylpentane, for example, ZSM-4, ZSM-20, ZSM-3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y and the rare earth metal-containing forms thereof, and a Lewis acid such as boron trifluoride, antimony pentafluoride or aluminum trichloride. The addition of a Lewis acid is reported to increase the activity and selectivity of the zeolite, thereby effecting alkylation with high olefin space velocity and low isoparaffin/olefin ratio.
U.S. Pat. No. 5,304,698 describes a process for the catalytic alkylation of an olefin with an isoparaffin comprising contacting an olefin-containing feed with an isoparaffin-containing feed with a crystalline microporous material selected from the group consisting of MCM-22, MCM-36, and MCM-49 under alkylation conversion conditions of temperature at least equal to the critical temperature of the principal isoparaffin component of the feed and pressure at least equal to the critical pressure of the principal isoparaffin component of the feed.
An additional difficulty with alkylation processes can be related to the availability and/or cost of the feeds for forming alkylate. Light paraffin feeds, such as a feed containing isobutane, are generally considered low cost feeds. However, the corresponding olefin feed for forming alkylate can generally be of higher cost, particularly when the corresponding olefin feed corresponds to a C3+ olefin feed, such as a feed of butene or isobutene, because these olefins are typically produced via dehydrogenation reaction which is a high temperature, thermodynamically limited process.
U.S. Pat. No. 5,243,084 describes a process for oxidation of isobutane to tertiary butyl hydroperoxide and tertiary butyl alcohol.
Thus, there remains a need for methods of producing alkylate from light paraffin feeds, which have greater selectively for higher octane rated branched alkanes and which can be produced without the use of liquid acids. Further, there remains a need for selective oxidation methods, which have increased conversion and selectively for producing tertiary alcohols, such as tert-butyl alcohol.